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# Edexcel S3 - Wednesday 25th May AM 2016 watch

1. (Original post by Zacken)
Yes. June 2013.
Thanks! done so many questions im losing track lol
2. (Original post by Zacken)
The order of ranking does not matter as long as it consistent.
(Original post by Inges)
No they've ordered both from smallest to largest, So for A the 2 means 2nd smallest in employee's and the 1 means 1st smallest in Population.
Thank you, I was just being a complete div
3. (Original post by Music With Rocks)
Thank you, I was just being a complete div
No problem, read all the questions and answers on here as your last resort & youll smash this don't worry at all!
4. (Original post by Inges)
If your spec is Edexcel then yes! Its real easy google it and memories it!
Please could you post this proof, can't seem to find it online, do we definitely need to be able to prove it? Thanks
5. What's the rule about mode mean and median in relation to positive and negative Skewness?
6. (Original post by Rkai01)
What's the rule about mode mean and median in relation to positive and negative Skewness?
Mean<Median<Mode = Negative
Mean>Median>Mode = Positive

Not sure how to learn it easily, i just learnt it how it is
7. (Original post by economicss)
Please could you post this proof, can't seem to find it online, do we definitely need to be able to prove it? Thanks
8. (Original post by Rkai01)
What's the rule about mode mean and median in relation to positive and negative Skewness?
mode<median<mean for positive

I remember it by the mean being the prime method used by people/statisicians so if the mean is highest, its positive
9. https://869d950bf149eefd5cd2652b4001...%20Edexcel.pdf
Question 3b, why is the variance the standard error and not 16 times the variance?
10. (Original post by economicss)
Please could you post this proof, can't seem to find it online, do we definitely need to be able to prove it? Thanks
I'm gonna write it out on a piece of paper and upload it in a minute.
11. I'm trawling through this thread and getting freaked out by people saying 'total error' and using terminology that isn't in the textbook so I'm gonna call it a day with this thread and revisit it after the exam tomorrow.

Good luck to everyone
12. (Original post by kennz)
mode<median<mean for positive

I remember it by the mean being the prime method used by people/statisicians so if the mean is highest, its positive
With relation to whether it can be from a normal distribution, is a positive Skewness indicating it can be from a normal distribution?
13. (Original post by kennz)
https://869d950bf149eefd5cd2652b4001...%20Edexcel.pdf
Question 3b, why is the variance the standard error and not 16 times the variance?
It asked Find the probability that the mean of these results is within 0.3 mm of w. and mean would be 16/16 square which make it /16
14. (Original post by anndz3007)
It asked Find the probability that the mean of these results is within 0.3 mm of w. and mean would be 16/16 square which make it /16
thank you, completely misread it, I thought thats what it had to be but I couldnt see the mean in the question haha
15. (Original post by Euclidean)
I'm trawling through this thread and getting freaked out by people saying 'total error' and using terminology that isn't in the textbook so I'm gonna call it a day with this thread and revisit it after the exam tomorrow.

Good luck to everyone
Good luck!
16. (Original post by economicss)
Pretty sure the textbook says the proof isn't examinable.
17. (Original post by Euclidean)
I'm trawling through this thread and getting freaked out by people saying 'total error' and using terminology that isn't in the textbook so I'm gonna call it a day with this thread and revisit it after the exam tomorrow.

Good luck to everyone
Sound.

Good luck.
18. (Original post by economicss)
Please could you post this proof, can't seem to find it online, do we definitely need to be able to prove it? Thanks
Its not letting me upload it so i put it on imgur.

19. For part d, if you use the Variance formula Var(X-Y)=Var(X)+Var(Y) you get 6sigma^2/5 which is incorrect. The actual variance was 4sigma^2/5 and I understand how to get there.

Am I correct in saying we do not use the variance formula because U1 and Ubar are from the same sample? Thanks.
Attached Images

For part d, if you use the Variance formula Var(X-Y)=Var(X)+Var(Y) you get 6sigma^2/5 which is incorrect. The actual variance was 4sigma^2/5 and I understand how to get there.

Am I correct in saying we do not use the variance formula because U1 and Ubar are from the same sample? Thanks.
It's because and are not independent. The formula you quoted are only for independent random variables . They are not independent because they come from the same sample, but the important thing here is that they are not independent.

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